Interpreting behavioral, biomedical, and psychological relationships in chronic disease from 2 x 2 tables using correlation.

Correlations of 0.3 and 0.4 in psychological studies in chronic illness (e.g. diabetes) have been criticized as having little clinical importance. The present article suggests that correlation coefficients be interpreted as binomial effect size displays (BESD) as a means of gleaning the clinical importance of a given correlation coefficient. The BESD is easily understood, computed, and applied to research in chronic disease. An illustration is provided in which a r of 0.2 is shown to correspond to a BESD in which the success rate is improved from 40 to 60%. Using BESD to interpret the meaningfulness of relationships, correlations as low as 0.2 may have clinical importance.